U.S. patent number 3,984,054 [Application Number 05/580,921] was granted by the patent office on 1976-10-05 for nozzle.
This patent grant is currently assigned to Barry Wright Corporation. Invention is credited to Alain Frochaux.
United States Patent |
3,984,054 |
Frochaux |
October 5, 1976 |
**Please see images for:
( Certificate of Correction ) ** |
Nozzle
Abstract
An air nozzle is provided which produces high thrust with low
noise. The nozzle is adapted to provide flow amplification by
inducing flow of ambient air with high pressure air.
Inventors: |
Frochaux; Alain (Boston,
MA) |
Assignee: |
Barry Wright Corporation
(Watertown, MA)
|
Family
ID: |
27053583 |
Appl.
No.: |
05/580,921 |
Filed: |
May 27, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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500647 |
Aug 26, 1974 |
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Current U.S.
Class: |
239/424;
239/DIG.21; 239/291; 239/DIG.7; 239/DIG.22 |
Current CPC
Class: |
B05B
1/005 (20130101); B05B 1/22 (20130101); B08B
5/02 (20130101); B05B 15/00 (20130101); G10K
11/161 (20130101); Y10S 239/07 (20130101); Y10S
239/22 (20130101); Y10S 239/21 (20130101) |
Current International
Class: |
B05B
1/00 (20060101); B05B 007/08 (); F01N 001/10 ();
F01N 001/14 () |
Field of
Search: |
;181/33HC,42,50,36A,43,51,64B,33HD,65,71
;239/DIG.7,DIG.21,DIG.22,291,314,418,422,423,424,424.5,587,265.13,588 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ward, Jr.; Robert S.
Attorney, Agent or Firm: Gilbert; Milton E.
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part application of my U.S.
Application Ser. No. 500,647 filed Aug. 26, 1974, now abandoned.
Claims
What is claimed is:
1. A high-thrust low-noise nozzle adapted to effect movement of a
secondary fluid by a pressurized primary fluid comprising, tubular
means forming a passageway having an entrance and an exit orifice,
said entrance being adapted for connection to a source of
pressurized primary fluid, at least one port communicating with the
passageway between said entrance and exit orifice, means
cooperating with said port for directing flow of primary fluid from
said port in a direction so as to induce flow of a secondary fluid
along the outside of said tubular means toward said exit, and
noise-reducing means positioned in said passageway between said
exit orifice and said port, said noise-reducing means creating
sufficient back pressure to force some of the pressurized pirmary
fluid to flow out of said passageway via said port.
2. A nozzle according to claim 1 wherein said noise-reducing means
comprises an element that is made up of a knitted metal wire mesh
fabric that has been convoluted and compressed and molded into a
self-supporting, dense, porous mass with the wire threads of said
fabric oriented randomly in said mass.
3. A high-thrust, low-noise nozzle comprising a body having means
defining a passageway, an entrance for admitting a pressurized
primary fluid to said passageway, and an exit at one end of said
body for discharging a stream of said primary fluid from said
passageway, said body also having an exterior surface that is
disposed so as to converge toward said passageway at said one end,
and flow inducing means including at least one port communicating
with said passageway between said exit and said entrance for
conducting some of the pressurized primary fluid out of said
passageway via said port and directing it along said surface toward
said one end so as to induce a secondary fluid surrounding said
body to flow along said surface and merge with the stream of
primary fluid discharged from said exit.
4. A nozzle according to claim 3 wherein said exterior surface
surrounds said passageway and is tapered toward said one end.
5. A nozzle according to claim 3 wherein said flow inducing means
comprises a second exterior surface on said body which is disposed
so as to converge toward said passageway away from said exit end,
and a transition surface that extends between said first and second
mentioned exterior surfaces.
6. A nozzle according to claim 5 wherein said flow inducing means
includes means spaced from said second exterior surface for
directing primary fluid to flow from said port along said second
exterior surface, so that substantially static secondary fluid
surrounding said second exterior surface is induced to flow with
primary fluid in turn over said transition surface and said first
mentioned surface.
7. A nozzle according to claim 6 wherein said spaced means
comprises an annulus surrounding and spaced from said body.
8. A nozzle according to claim 7 wherein said annulus surrounds the
portion of said body that includes said port.
9. A nozzle according to claim 3 including a fluid-permeable
element in said passageway between said exit and said port.
10. A nozzle according to claim 9 wherein said fluid permeable
element comprises a compressed mass of a wire mesh fabric.
11. A nozzle according to claim 9 wherein said fluid permeable
element is made so as to effect substantially laminar flow of the
stream of pressurized primary fluid discharged from said exit.
12. An amplifier nozzle adapted to effect movement of a secondary
fluid by a pressurized primary fluid so as to produce a stream made
up of said primary and secondary fluids, said nozzle comprising an
elongate body having a first tapered section at one end thereof, a
second oppositely tapered section, a transition section contiguous
with and joining said first and second tapered sections, an end
section at one end, and a throat section contiguous with and
joining said second tapered section to said end section, a
longitudinally extending bore in said body forming a passageway
extending through said sections, an inlet at said opposite end of
said body for admitting a pressurized primary fluid to said
passageway and an exit at said one end for discharging a stream of
said primary fluid from said passageway, a shell attached to said
end section, said shell surrounding but spaced from said throat
section and at least part of said second tapered section, a chamber
between said shell and said throat section, at least one port in
said throat section for conducting primary fluid from said
passageway into said chamber, and a narrow orifice formed between
said shell and said second tapered section for conducting primary
fluid in a thin stream out of said chamber and along said second
tapered and transition sections so as to induce a static secondary
fluid surrounding said shell to flow with said thin stream of
primary fluid along said first tapered section toward said one end
of said body and combine with the stream of primary fluid
discharged at said exit.
13. A high-thrust low-noise nozzle adapted to effect movement of a
secondary fluid by a pressurized primary fluid comprising, tubular
means forming a passageway having an entrance and an exit orifice,
said entrance being adapted for connection to a source of
pressurized primary fluid, at least one port communicating with the
passageway between said entrance and exit orifices, at least one
other port communicating with said passageway between the first
mentioned port and said exit orifice, means cooperating with said
first mentioned and one other ports for directing flow of primary
fluid from each of said ports in a direction so as to induce flow
of a secondary fluid along the outside of said tubular means toward
said exit, and noise-reducing means positioned in said passageway
between said exit orifice and said one other port for effecting
substantially laminar flow of the stream of pressurized primary
fluid discharged from said exit orifice, said noise-reducing means
creating sufficient back pressure to force some of the pressurized
primary fluid to flow out of said passageway via said first
mentioned and one other ports.
14. A high-thrust, low-noise nozzle comprising a body having means
defining a passageway, an entrance for admitting a pressurized
primary fluid to said passageway, and an exit at one end of said
body for discharging a stream of said primary fluid from said
passageway, said body also having first and second exterior
surfaces that are disposed so as to converge toward said passageway
at said one end, and flow inducing means including at least two
ports, one of said ports communicating with said passageway between
said exit and said entrance for conducting some of the pressurized
primary fluid out of said passageway via said one port and
directing it along said first surface toward said one end so as to
induce a secondary fluid surrounding said body to flow along said
first surface, and the other of said ports communicating with said
passageway between said exit and said one port for conducting some
of the pressurized primary fluid out of said passageway via said
other port and directing it along said second surface toward said
one end to induce more of said secondary fluid surrounding said
body and the said fluids flowing along said first surface to merge
with the stream of primary fluid discharged from said exit.
15. A nozzle according to claim 14 wherein each of said first and
second exterior surfaces is concentric with said passageway and is
tapered toward said one end.
16. A nozzle according to claim 15 wherein said first and second
exterior surfaces have the same slope and are substantially
coincident with one another.
17. A nozzle according to claim 14 wherein said flow inducing means
comprises a third surface on said body which is disposed so as to
converge toward said passageway away from said exit end, and a
fourth transition surface that extends between said first and third
exterior surfaces.
18. A nozzle according to claim 17, wherein said flow inducing
means further includes a fifth surface on said body which is
disposed so as to converge toward said passageway away from said
end, and a sixth transition surface that extends between said
second exterior surface and said fifth surface.
19. A nozzle according to claim 18 wherein said sixth transition
surface is cylindrical.
20. A nozzle according to claim 18 including means cooperating with
said sixth transitional surface to form an orifice between said
first and second surfaces.
21. A nozzle according to claim 14 including a fluid-permeable
element in said passageway between said exit and said ports.
22. A nozzle according to claim 21 wherein said fluid-permeable
element comprises a compressed mass of a wire mesh fabric.
23. An air nozzle comprising:
a body including an interior elongated passageway having at one end
thereof an entrance for admitting pressurized primary fluid and at
the other end thereof an exit for discharging said primary
fluid;
at least one port providing an opening between the exterior of said
body and said passageway at a point intermediate said entrance and
exit;
means for creating sufficient back pressure to force some of the
pressurized primary fluid to flow out of said passageway via said
at least one port;
a surface on the exterior of said body which converges with said
passageway toward said exit; and
means for directing pressurized primary fluid conducted out of said
at least one port along said surface toward said exit so as to
induce secondary fluid surrounding said body to flow and merge with
the primary fluid discharged from said exit.
Description
This invention relates to fluid delivery nozzles and more
particularly to nozzles which exhibit high thrust and low
noise.
Various types of fluid delivery nozzles have been proposed for use
in manufacturing establishments where a stream of air is directed
to perform a function such as ejecting parts of blowing refuse from
a machine or work station. In such applications, it is desirable
that the stream be concentrated and that the working force of the
stream be substantial. In this respect the prior art is exemplified
by U.S. Pat. Nos. 3,129,892, 3,599,876, 3,814,329, 3,647,142,
3,263,934, 3,743,186, 3,801,020, 3,806,039 and 3,795,367, and the
references cited in the files of said patents. However, many well
known types of nozzles have been finding increasing objection in
view of recently enacted health and safety regulations. A
particular objection to many existing nozzles is that they produce
uncomfortable, and in some cases unbearable, noise levels. This is
due to the fact that in most factories or shops where pneumatically
operated equipment is employed, the compressed air lines will have
an air pressure ranging from about 90-125 psi. Accordingly, the
high pressure jets tend to produce unreasonably high noise levels.
While some air nozzles have been devised which exhibit reduced
noise levels, they do not reduce the noise levels to an acceptable
level or else achieve reduced noise levels at the expense of
reduced thrust or other limitations.
Accordingly, a primary object of this invention is to provide a
nozzle which exhibits high thrust and low noise levels.
A further object of this invention is to provide a nozzle of the
character described wherein ambient air is induced into an air
stream by use of high pressure air so as to provide a stream having
an effective working force or thrust.
Still another object is to provide a nozzle which is extremely
simple in construction, reliable and durable in use and economical
to manufacture.
The foregoing objects and other objects hereinafter disclosed or
rendered obvious are achieved by providing a nozzle which comprises
an inlet for connection to a source of high pressure air, an air
passageway for conducting an air stream from the inlet to a nozzle
discharge opening, at least one group of one or more ports
intermediate the inlet and the discharge opening for conducting
pressurized air out laterally from the passageway, and means
including an appropriately shaped outer nozzle surface for causing
the compressed air exiting the one or more ports to induce a flow
of amibent air along the outer surface of the nozzle toward the
nozzle's exit end so as to provide a working stream which combines
the pressurized air discharged from the main passageway and the
induced ambient air. Since the mass of the resulting working stream
is greater than that of just the pressurized air stream which exits
the passageway, it accordingly enhances the working force of the
combined stream substantially over that of only the discrete
pressurized air stream which exits the passageway. A selected
air-permeable flow-modifying element is disposed in the passageway
for the purpose of causing the stream flowing in the passageway to
assume a laminar flow characteristic, whereby to reduce noise while
at the same time permitting the air stream in the passageway to
exit the nozzle at a high velocity. The flow-modifying element also
provides a back pressure which forces air to exit the passageway
via the one or more ports whereby to induce ambient air to flow
along the outer nozzle surface toward the nozzles exit.
Other features and many of the attendant advantages of this
invention are disclosed by the following detailed description which
is to be considered together with the accompanying drawings,
wherein:
FIG. 1 is a longitudinal section of a preferred embodiment of the
invention;
FIG. 2 is a diagrammatic view on an enlarged scale of a piece of
knitted metal wire mesh;
FIG. 3 is a sectional view of a die for forming the flow-modifying
element; and
FIG. 4 is a longitudinal section of a second embodiment of the
invention.
The same numerals are used in the several figures to designate
identical parts.
The present invention makes use of a modification of the Coanda or
wall attachment principle to entrain ambient air in a high velocity
small mass air stream. As disclosed by Coanda U.S. Pat. Nos.
2,052,869 and 3,047,208, and as exemplified in nozzle applications
by U.S. Pat. Nos. 3,743,186, 3,801,020, 3,806,093 and 3,795,367,
the Coanda effect basically involves discharging a small volume of
a primary fluid under a high velocity from a nozzle having a shaped
surface adjacent the nozzle, whereby the stream of primary fluid
tends to follow the shaped surface and as it does, it induces a
surrounding secondary fluid -- notably, ambient air -- to flow with
it along the shaped surface. The result is that an exhaust stream
is produced which combines both fluids. Thus nozzles constructed in
accordance with the principles established by Coanda exhibit high
thrust due to the amplification in flow produced by the Coanda
effect. However, existing Coanda effect nozzles do not have a
satisfactory noise limiting capability or else are expensive to
manufacture. Hence, for reasons of comfort with respect to noise as
well as cost, other type of nozzles tend to be preferred in many
installations even though they exhibit less thrust or achieve
comparable thrust at the expense of greater consumption of
pressurized air.
It has been recognized that in nozzles, high thrust tends to give
high noise levels and low noise levels can be achieved only at the
expense of reduced thrust. The problem of achieving both high
thrust and low noise levels may be explained by considering the
mathematical statements governing thrust and acoustical power for a
nozzle. The pertinent statements for thrust and acoustical power
are respectively as follows: ##EQU1## and ##EQU2## where T = thrust
in pounds;
W = weight flow rate (lb/sec);
g = acceleration due to gravity (ft/sec.sup.2);
u = air stream velocity (ft/sec);
W.sub.AC = acoustical power (watts); and
c = local velocity of sound in medium (ft/sec).
The acoustical power (noise emitted) of a nozzle increases by a
factor of air stream velocity to the seventh power whereas thrust
increases by a factor of velocity to the first power. Therefore,
from the foregoing mathematical statements, it is apparent that a
possible way to increase thrust without substantially increasing
noise is to increase the weight flow rate without increasing the
air stream velocity. However, such a solution cannot be adapted in
practice to a straight nozzle because of size limitations. This can
be seen from the following equations:
where
W = weight air flow (lb/sec);
Q = air flow rate (ft.sup.3 /sec);
d = local air density (lb/ft.sup.3);
u = air stream velocity (ft/sec); and
A = cross-sectional area of nozzle orifice (ft.sup.2)
Since the local air density is substantially constant, increasing
the weight flow rate by increasing the air flow rate, while
maintaining a relatively small flow velocity, can be achieved only
by increasing the cross-sectional area of the nozzle orifice, but
this has severe practical limitations in nozzles for industrial
blow-off or ejection applications. Therefore, the only practical
solution is to use a form of air amplifier whereby ambient air is
drawn into the main air stream while keeping the flow through the
orifice of the nozzle at a minimum.
The present invention provides a nozzle that is similar to the
Coanda-type nozzles disclosed by U.S. Pat. Nos. 3,743,186,
3,795,367, 3,801,020 and 3,806,039 in that it involves air
amplification, but it differs therefrom in that the air
amplification is achieved by combining the pressurized air and the
ambient air outside of and downstream of the exit orifice of the
nozzle. It also differs in that flow-modifying means are provided
for reducing the noise of the pressurized air stream flowing
through the nozzle and producing a laminar jet at the exit orifice,
whereby induced ambient air flowing around the outside of the
nozzzle can blend with the main jet stream without creation of
noise producing eddies and vortices.
Turning now to FIG. 1, the illustrated nozzle comprises a bushing
or housing 2 which has a reduced diameter threaded extension 4 for
connection to a conduit 6 which leads to a source (not shown) of a
pneumatic medium such as compressed air. The main portion of the
bushing is in the form of a cylindrical shell 8 which has a
cylindrical outside surface 10. The inside of shell 8 comprises an
annular end surface 12, a cylindrical surface 14 that extends
forwardly of end surface 12, and a frustoconical surface 16 which
forms an outwardly tapered or flared opening for the shell. The end
section 18 of the shell and the threaded extension have a common
centrally located and smooth surfaced bore 20 that has a circular
cross-section and serves as an inlet and a flow passageway for the
pressurized pneumatic medium.
Attached to the bushing 2 is a nozzle element identified generally
as 22. The latter has a centrally located smooth-surfaced bore 20A
that is the same size as and is aligned with bore 20. Nozzle
element 22 comprises an end section 24, a throat section 26, and a
main section 28. End section 24 has a flat annular rear surface 30,
a cylindrical outer surface 32, and a flat annular front end
surface 34. Surface 32 is sized to make a tight friction fit with
the inner surface 14 of the shell. Throat section 26 has a
cylindrical outer surface 36 that has a smaller diameter than
surface 32 whereby to provide an annular chamber 38 between it and
the shell. Additionally, the throat section has at least one and
preferably several ports 40 that lead from bore 20A to chamber 38.
Preferably, but not necessarily, the axes of ports 40 extend at a
right angle to bore 20A.
The exterior of main section 28 has a generally bulbous shape
characterized by a rear frusto-conical surface 42, a front
oppositely tapered frusto-conical surface 44, and a convex
circumferentially-extending transition surface 46. The nozzle
section is sized so that its rear outside surface 42 is spaced from
the adjacent surface 16 of the shell. Preferably the shape of the
rear frusto-conical surface 42 is linear and is set so that, with
increasing distance from throat section 26, it converges toward the
adjacent surface 16 of the shell, whereby to form an annular
passageway or orifice 48 that communicates with chamber 38 and
whose cross-sectional area decreases progressively with increasing
distance from chamber 38. Preferably, but not necessarily, the
axial length of the outer surface of the annular throat section is
set so that its junction with surface 42 is aligned radially with
the junction of surfaces 14 and 16 of the shell, as shown. The
frusto-conical surface 42 preferably is long enough so that its
forward end projects radially beyond the outer surface of the
shell, whereby the transition surface 46 is in position to
intercept ambient air flowing along the outer surface of the
bushing toward the nozzle element. The convex transition surface 46
preferably has a smooth circular curvature in longitudinal section,
but the convex curvature could be formed according to a parabolic
or other suitable function. The frusto-conical surface 44 is formed
so that its front end terminates close to the axial bore 20A.
Preferably, its front end intersects or nearly intersects the axial
bore so that the nozzle element has a relatively narrow front edge
as shown at 50. While a relatively thin knife edge may be
advantageous for optimum merging of ambient air with the air stream
exiting from bore 20A, it is preferred that edge 50 be somewhat
blunt so as to minimize possible injury to workmen. In any event,
the slope and length of surface 44 are set so that the inducted
ambient air and the pressurized air stream from bore 20A will merge
in a smooth transition without the creation of noise producing
eddies and vorteces.
It also is essential that the slopes of confronting surfaces 16 and
42 and the minimum gap therebetween be set so that air will exit
the orifice 48 as a thin film which will tend to adhere to and flow
along surface 42 over surface 46 and along surface 44 in the manner
shown by the arrows 52. By way of example, in a preferred
embodiment of the invention, the surface 44 has a slope of about
20.degree. with respect to the common axis of bores 20 and 20A,
surfaces 16 and 42 have slopes with respect to the same axis of
20.degree. and 30.degree. respectively, and the gap between
surfaces 16 and 42 is between about 0.003 and 0.006 inch.
It is also essential, for better promotion of laminar flow and to
reduce noise, that the bore 20A have a diameter substantially the
same as or smaller than bore 20. Preferably bores 20 and 20A are
the same size and the end surfaces 12 and 30 engage one another as
shown, since this arrangement provides a smooth transition from
bore 20 to bore 20A and thus avoids creation of eddies and
turbulence in the air stream as it passes into bore 20A. Making
bore 20A larger than bore 20 allows the pressurized pneumatic
medium to expand as it passes into bore 20A, and such expansion
promotes turbulence and creates noise.
Also forming part of the nozzle assembly is a flow-modifying
noise-reducing element 54 which is essentially a cylindrically
shaped plug and preferably, but not necessarily, is formed with
flat end surfaces as shown. Noise-reducing element 54 is made of a
knitted wire mesh fabric and may be formed in situ or preformed and
installed after formation.
The element 54 is made generally in accordance with the teachings
of U.S. Pat. No. 2,334,263 issued Nov. 16, 1943 to R. L. Hartwell
for Foraminous Body and Method of Producing Same. Element 54
consists of a compressed mass of metal wire charactrized by a
closely packed, interlocked wire structure that forms a coherent
body. The element is fabricated from knitted metal wire mesh of
selected gauge. The mesh may be knit flat or tubular and may be of
selected mesh loop size. Preferably it is knitted as a tube or sock
on a circular knitting machine. In its simplest form, the knitted
wire mesh tube may be knitted from a single continuous length of
metal wire which is so manipulated as to form a continuous tube in
which successive turns of the wire form lengths which extend
circumferentially of the tube and are interlocked by stitches. Each
length is bent locally beyond its elastic limit as a result of the
formation and interlocking of loops or stitches as the tube is
knitted. Thus each circumferential length, in effect, forms a
flattened spring which may be stretched or compressed. The finished
tube or sock is flattened longitudinally so as to form a two-ply
ribbon. Preferably, but not necessarily, the flattened tube may be
corrugated traversely to provide further interlocking between the
lengths of wire in the plies thereof. Corrugating the fabric is
known in the art as "crimping" and the product is commonly called
"crimped knitted wiremesh fabric". The tube may be corrugated at a
right angle to its axial length or at a different angle, e.g.,
45.degree., in the manner disclosed by the Hartwell patent. FIG. 2
presents a side view of a portion of a knitted wire mesh fabric
tube as above described. The fabric is seen to comprise
circumferential turns of wire 56 with each turn having loops or
stitches which are interlocked with adjacent turns. In this case,
the fabric is crimped along spaced diagonal lines 58.
Knitted wire mesh fabric and the method of making the same are well
known (in this connection see also U.S. Pat. Nos. 3,346,302,
2,680,284, 2,869,858 and 2,426,316).
In the practice of this invention, the knitted wire mesh fabric is
preferably made of a stainless steel wire, although other steels
and alloys may be used.
Preferably the flow-modifying element 54 is made by flattening a
knitted wire mesh fabric tube upon itself to form a flat two-ply
ribbon, and then rolling the ribbon upon itself. The ribbon is
wound up in the manner shown in FIG. 2 of U.S. Pat. No. 3,346,302
(except that it is not wound upon a mandrel) and FIG. 2 of the
Hartwell patent, with the result that the rolled up body is
generally cylindrical to the width or transverse dimension of the
ribbon extends parallel to the body's longitudinal axis. More
specifically, the cylindrical body consists in cross-section of a
continuous spiral convolute. In this generally cylindrical body the
lengths of wire making up each turn of the fabric tube are now
largely so oriented as to extend from one end of the body to the
other in directions generally parallel with the body's longitudinal
axis. This cylindrical body is then compressed and molded into a
flow-modifying noise-reducing element of desired density and
shape.
FIG. 3 shows a forming die assembly made of tool steel for forming
the element 54 in situ. The forming die assembly comprises a
stationary die 60 having a cavity 62 shaped to receive the forward
portion of the main section 28 of the nozzle element and a
cylindrical extension 64 at the base of the cavity which is sized
to fit snugly within the bore 20A. The upper surface of extension
64 has a flat end surface 66. A die sleeve 68 fits down over the
rear portion of main section 28 and seats on the flat upper surface
70 of die 60. Sleeve 68 makes a close fit with the surfaces 42 and
32 of the nozzle element and is held against lateral movement by
dowels 74 which are embedded in the upper surface 70 of the die and
make a sliding fit in holes in the sleeve. The die assembly also
comprises a piston unit consisting of an elongate piston 76 and a
piston head 78 secured to the piston by a screw 80. The bottom end
of piston 76 is enlarged and has a cylindrical outer surface 82
sized to make a close sliding fit with bore 20A.
In molding the element 54 in situ, the die assembly is mounted in a
press (not shown) having a stationary bed and a vertically
reciprocal pressure head, with the die member 60 being fixed to the
bed and the piston assembly being mounted to the pressure head in
vertical alignment with the die member. With the die assembly open,
the nozzle element is inserted in the cavity of die 60 and sleeve
68 is positioned as shown so as to hold the nozzle element
centered. Then the rolled-up or folded knitted wire mesh fabric is
inserted into the upper end of the nozzle element and the piston
unit is operated to drive the fabric body into the housing. The
length of knitted wire mesh fabric tube employed in forming the
element 54 is set so that when the element is formed it has a
density which is a predetermined percentage of the density of the
metal of which the wire mesh fabric is made. The cylindrical wire
mesh body formed by rolling up the flattened wire mesh fabric tube
is inserted in the bore 20A so that the rolled up layers of the
wire mesh fabric tube extend axially of and are compressed radially
by the surrounding surface of the nozzle element, i.e., the
cylindrical knitted mesh body is inserted so that its axis of
convolution extends parallel to the axis of bore 20A. The fabric
body is compressed and molded by the compressive co-action of die
extension 64 and the end of the piston 76. The extent of
penetration of the piston unit determines the final size and
density of the mass 54 of knitted wire mesh fabric, and preferably
the desired density is achieved when the piston unit bottoms on the
upper end of die sleeve 68. The formed element 54 and housing
nozzle element 22 are tightly gripped together by a friction fit
and the element is self-supporting and has excellent structural
integrity.
The nozzle element in the embodiment just described is preferably
made of material that is softer than the material of which the
element 54 is made. Preferably, nozzle element 22 is made of
aluminum or an aluminum alloy while element 54 is made of stainless
steel knitted wire mesh. As a consequence, as the element 54 is
formed in situ, portions of the wire of which it is made will
abrade and in some places actually cut into the interior surface of
the nozzle element, with the result that the element is
mechanically interlocked with the housing. Additionally, the formed
element has a certain amount of spring action and as a consequence,
it exerts a radial force against the surrounding nozzle element
which further improves the mechanical gripping action between the
two parts. A connection of almost equal strength can be achieved
between the nozzle and element 54 where the latter is preformed
since the preformed element also has a certain spring action.
Accordingly, by making the preformed element slightly oversized, it
is possible to assure a strong press-fit connection to the nozzle
element. Again due to the difference in materials hardness, as the
preformed element is forced into bore 20A, portions of the wire of
which it is formed will abrade and cut into the interior surface of
nozzle element 22 so that it is mechanically interlocked with the
nozzle element.
The bushing 2 may be made of the same material as the nozzle
element or a different material. Thus, for example, if nozzle
element 22 is made of aluminum, bushing 2 may be made of aluminum
or stainless steel. The bushing may be, and preferably is, secured
to the nozzle element by a press-fit as previously described, or it
may be secured by other means known to persons skilled in the
art.
As the rolled up or convoluted body of knitted wire mesh fabric is
compacted and molded into the element 54, it is tightly compressed
in directions transverse to the width of the flattened tube or
ribbon, i.e., it is compressed both radially and axially, with the
result that the turns or length of wire are crimped at innumerable
points beyond their elastic limits so that they take a more or less
permanent set. Additionally, as the wire mesh fabric is compressed,
the wire is so deformed as to produce a compressed mass or body
consisting of a very great number of uniformly distributed,
randomly directed, relatively short spans or lengths of wire which
contact each other at innumerable points within the mass, with the
result that these spans or lengths are intimately interlocked
substantially uniformly throughout the entire volume of the mass
with portions of the spans of wire being spaced to form small
pockets and passageways of capillary size. The net result is a
relatively dense yet porous cohesive or self-supporting body
consisting of fine, intermingled and interconnected spring wire
spans and characterized by substantial structural integrity,
controlled density, a uniform and fine porosity, and a controlled
spring constant. The multiplicity of short spans of wire, the
uniformity of distribution and random directions of such spans, and
the innumerable points of contact between them, all contribute to
the capability of the element to modify the flow of air through
bore 20A so that it will exit the nozzle as a laminar flow jet
stream.
Operation of the device of FIG. 1 as an air nozzle will now be
described. Compressed air enters the nozzle through the conduit 6,
flows along bores 20 and 20A and through the element 54, and
escapes via the exit orifice defined by annular end surface 50 of
the nozzle element. Since the wire mesh plug 54 offers some
resistance to free flow of the compressed air, a back pressure is
created upstream of the element. Consequently, part of the
pressurized air supplied to bore 20 is diverted out of the bore
through ports 40 into chamber 38 and then flows out of chamber 38
via the small gap annular orifice formed between surfaces 16 and
42. In passing out of this small gap orifice, the pressurized air
forms a very thin film moving at a high velocity. Since air moving
at a high velocity has a static pressure less than atmospheric
pressure, a partial vacuum is created which on one side makes the
air film cling to and follow the exterior contour of the nozzle
element as shown by the arrows 52, and on the other side draws in
ambient air as shown by arrows 57. The thin air film and the
induced ambient air flow along surface 44 and merge with the air
stream discharged from bore 20A, thus in effect amplifying the air
flow directed by the nozzle. It is to be noted that the transition
surface 46 is located wholly to one side of the line of discharge
of air from the narrow gap orifice 48 formed between surfaces 16
and 42, and this transition surface (and whatever portion of
surface 42 projects beyond the outer end of surface 16) acts to
guide the air flowing out of orifice 48. A differential pressure
effect is created which causes the air film to attach itself to the
exterior surface of the nozzle element and induces the ambient air
to follow the path of the thin film. As indicated earlier, the
element 54 modifies the flow of air in bore 20A so that the main
compressed air stream forms a laminar jet on passing through that
element and out of the nozzle. Element 54 thus reduces the noise
produced by the compressed air flowing out of the nozzle via bore
20A and a further noise reduction occurs because the laminar jet
allows the induced air flowing around the nozzle to combine with it
in a smooth transition without any noise-producing eddies and
vortices.
The following example illustrates the extent of noise reduction and
the magnitude of the thrust achieved by the present invention. A
nozzle was made having a construction as shown in FIG. 1. The bores
20 and 20A had a diameter of 0.312 inch, and two diametrically
opposed ports 40 were provided having a diameter of 0.09 inch. The
gap at the exit end of orifice 48 measured about 0.003 inch and the
surfaces 42 and 44 extended at angles of 30.degree. and 20.degree.
to the axis of bore 20A. The curvature of surface 46 in
longitudinal section was substantially that of a circular arc and
its apex was about 0.45 inches from the axis of bore 20A. The
nozzle element 22 and bushing 2 were made of aluminum and the
element 54 was made of two-ply stainless steel knitted wire mesh
ribbon. Element 54 was formed in-situ in the manner above described
and in its as-formed condition had a density of 40% of the density
of the stainless steel wire making up the knitted wire mesh fabric.
Element 54 had an axial length of about 0.25 inch. The bushing 2
was connected to a 100 psi pressurized air supply and the noise and
thrust of the nozzle were determined according to well known
techniques. The noise level was measured at a point about 36 inches
downstream of the nozzle. The noise level was found to be 81dBA and
the thrust was found to be 1.0 lbf, and the flow through the nozzle
was 29 scfm. By way of comparison, the noise produced by air
discharged at the rate of 29 scfm from an ordinary pipe having the
same internal diameter as bore 20A was found to be about 99dBA and
the thrust was about 0.95lbf.
It is to be appreciated that for certain applications it may not be
necessary to effect any noise reduction or to provide the degree of
noise reduction achieved with preferred embodiments of the
invention. Thus, the invention may be practiced without the use of
noise-reducing element 54 constructed as above described.
An air nozzle having a construction as shown and described in FIG.
1 thus exhibits relatively high thrust and low noise levels. In
order to provide even greater thrust while maintaining
substantially low noise levels, the air nozzle of the present
invention may be modified to include a second amplifying stage.
Referring to FIG. 4, an air nozzle similar to the nozzle shown in
FIG. 1 and modified to include such a second stage is illustrated.
The two-stage nozzle comprises a housing 2A which has a reduced
diameter threaded portion 4A for connection to the pressurized air
conduit 6A. The housing 2A includes a cylindrical shell 8A which is
similar to the shell shown and described in the FIG. 1 embodiment.
The shell 8A, however, has been modified to include one
radially-extending hole which is located forwardly of end section
18A and extends through the surfaces 10A and 14A for accommodating
a roll pin 102.
A nozzle element 22A similar to the nozzle 22 of FIG. 1, is
attached to the housing 2A. The nozzle element 22A, thus includes
an end section 24A, throat section 26A, and a main section 28A. End
section 24A has been modified to include at least one radially
directed hole for accommodating the roll pin 102 so that the nozzle
element is restrained from axial movement with respect to shell 8A.
The throat section 26A includes at least one, and preferably a
plurality of ports 40A which communicate with the annular chamber
38A which in turn communicates with passageway 48A. The latter is
defined by the space between the surface 16A of shell 8A and the
main section 28A.
Main section 28A, which is provided with the front and rear
frusto-conical surfaces, 42A and 44A, respectively, and the
transition surface 46A, is modified to include at least one
radially-directed hole which extends from transition surface 46A
entirely through main section 28A for accommodating a roll pin 104.
The front interior end of the nozzle element 22A is provided with a
counter bore 106 which forms a radially-directed annular shoulder
108 with the bore 20A of the nozzle element.
In order to provide even greater thrust while maintaining low noise
levels, a second nozzle element, identified generally at 22B, is
attached to the element 22A. The second nozzle element 22B is
disposed in counterbore 106 and has a centrally-located
smooth-surfaced bore 20B which is aligned with bore 20A and
countersunk at the rear as shown at 110. The front end of bore 20B
is provided with a flow-modifying noise reducing element 54A, the
latter being made, formed and installed in the same manner as
element 54 previously described.
The nozzle element 22B also includes an end section 24B, a throat
section 26B and a main section 28B. The end section 24B has a flat
annular rear surface 112 which contacts the shoulder 108, and a
cylindrical outer surface 32B which is sized to make a tight
friction fit with the inner surface of counterbore 106. The end
section 24B is modified to include a radially-directed hole for
accommodating the roll pin 104 so that the second nozzle element
22B is restrained from axial movement with respect to the first
nozzle element 22A.
The throat section 26B includes at least one, and preferably a
plurality of ports 40B which communicate with the annular chamber
38B provided between the throat section 26B and the surface of
counter bore 106. The annular chamber 38B in turn communicates with
an annular orifice or passageway 48B which is defined by the space
between the surface of counter bore 106 and the main section
28B.
The exterior of the main section 28B generally has a shape which is
similar to the bulbous shape of main section 28A, in that it
includes front and rear frusto-conical surfaces, 44B and 42B,
respectively, which are of the same slope as the respective
surfaces 42A and 44B. The section 28B has been modified however so
that the transition surface 46B is a cylindrical,
circumferentially-extending surface. The second nozzle element 22B
is sized so that the front frusto-conical surface 44B is
substantially coincident with front surface 44A and intersects the
counter bore 106 at annular end surface 50A.
The slope and length of front surface 44B are set so that the
ambient air and the pressurized air stream exiting bore 20B will
merge in a smooth transition without the creation of noise
producing eddies and vortices.
It is also essential that the gap between the surface of the
counterbore 106 and the cylindrical surface 46B of the nozzle
element be set so that air will exit the orifice 48B as a thin film
which will tend to join with the flow of ambient air along surface
44A of the first nozzle element and surface 44B of the second
nozzle element. By way of example, in a preferred embodiment of the
two stage amplification device the surfaces 44A have a slope of
about 20.degree. with respect to the common axis of bores 20A and
20B, surface 42B has a slope with respect to the same axis of about
33.degree., and the gap between the cylindrical surface of
counterbore 106 and cylindrical surface 46B of the second nozzle
element between about 0.003 and 0.006 inch.
In order to promote laminar flow and reduce noise, the largest
diameter of the countersink 110 of the second nozzle is
substantially the same as or smaller than bore 20A, while the
diameter of the bore 20B is smaller than bore 20A. Preferably, the
largest diameter of the countersunk portion 110 and the diameter of
bore 20A are the same size and the end surfaces 108 and 112 engage
one another as shown, since this arrangement provides a smooth
transition from bore 20A to bore 20B and thus substantially avoids
creation of eddies and turbulence in the air stream as it passes
into bore 20B.
Operation of the two stage amplification device of FIG. 4 as an air
nozzle will now be described. Compressed air enters the nozzle
through the conduit 6A, flows along bores 20, 20A and 20B and
through element 54A, and escapes via the exit orifice defined by
annular end surface 50B of the second nozzle element. As previously
described, since the wire mesh plug 54A offers some resistance to
free flow of the compressed air, a back pressure is created
upstream of the element. Consequently, part of the pressurized air
supplied to bore 20A is diverted through ports 40A into chamber 38A
and then flows out of chamber 38A via the small gap annular orifice
48A between surfaces 16A and 42A. In passing out of this small gap
orifice 48A, the pressurized air forms a very thin film moving at a
high velocity, which clings to and follows the exterior contour of
the nozzle elements 22A as shown by the arrows 52A and draws in
ambient air as shown by arrow 57A, as previously described in
reference to FIG. 1.
Simultaneously, the back pressure created upstream by the presence
of element 54A causes part of the pressurized air supplied to bore
20B to be diverted out of the bore through ports 40B into chamber
38B formed between the cylindrical surface 46B of the second nozzle
element 22B and the surface of counterbore 106. In passing out of
orifice 48B, the pressurized air forms another very thin film
moving at high velocity. Since the static pressure of this thin
film of air is less than atmospheric pressure, a partial vacuum is
created which on one side makes the air film cling to and follow
the exterior contour of the second nozzle element 22B as shown by
arrows 52B and on the other side draws ambient air as shown by
arrows 57B. The thin air film provided by orifice 48B and the
induced ambient air as shown by arrows 57B is guided over
transition surface 44B together with the air stream from the first
stage represented by arrows 52A and 57A. Thus, the additional
annular orifice which is introduced by the second amplification
stage increases the thrust of the nozzle while maintaining low
noise levels.
It is to be appreciated that for certain applications it may not be
necessary to effect any noise reduction or to provide the degree of
noise reduction achieved with preferred embodiments of the
invention. Thus, the invention may be practiced without the use of
noise-reducing elements 54 or 54A constructed as above described.
If noise is of no consequence, elements 54 and 54A are entirely
omitted, and in the FIG. 1 embodiment bore 20A must be modified to
create the needed back pressure. This can be achieved in various
ways, e.g., by forming bore 20A with a reduced diameter section
downstream of ports 40 or providing it with a baffle or other
obstruction member for impeding air flow and thus creating a
suitable back pressure. In the FIG. 4 embodiment the needed back
pressure may be provided by the fact that bore 20B is of a smaller
diameter cross section with respect to bore 20A.
Obviously the nozzle may be made other than as herein shown and
described. Thus, for example, the shape and dimensions of the
nozzle element and the bushing may be varied and the latter may be
adapted to be secured to a conduit by other than a screw
connection. In the device of FIG. 1, a roll pin similar to pin 102
also may be used to secure nozzle 22 to shell 8. Also, more than
one noise-reducing element may be installed in bore 20A (FIG. 1) or
20B (FIG. 4) as disclosed by co-pending U.S. Pat. Application
Serial No. 388,636, filed Aug. 15, 1973 by Alain Frochaux and
Charles M. Salerno for Noise-Reducing Fluid-Flow Devices.
Furthermore, while the illustrated nozzle is intended for use with
air, it also may be used as a nozzle for other fluids.
* * * * *